This invention relates to food thawing apparatus and, more particularly, to apparatus which is adapted for incorporation in a household refrigerator or freezer which operates to thaw frozen food using high-frequency electromagnetic energy.
The advantages of freezing food for preservation purposes are offset to some extent by the need to thaw the frozen food before it can be made ready for food preparation. In general, the need to thaw certain foods before cooking or making use of it in food preparation procedures is well known.
Typically, thawing of frozen food can be accomplished by allowing the food to stand at room temperature until it is fully thawed. In some cases, it is recommended that the frozen food be placed in the fresh food compartment of a refrigerator until thawed. Depending on the size of the food package, this procedure can be very time-consuming and when allowed to stand at room temperature, the timing must be such that the food is used promptly upon thawing or else immediately placed back into the refrigerator to avoid the possibility of food spoilage.
Microwave ovens are currently available that have provision for a low power setting intended to permit thawing of frozen food by means of electromagnetic radiation of energy into the food load. Although somewhat beneficial for this purpose, the microwave oven has certain drawbacks when used for defrosting frozen food. Typically, microwave ovens operate at extremely high frequency such as 915 MHz or, more commonly, 2450 MHz. As is well known, depth of penetration of the electromagnetic energy into a food load is proportional to the wavelength and at the frequency of 2450 MHz, at which most defrost operations are currently performed, the penetration at the low energy levels used for defrosting can be as shallow as one quarter inch. Thus heating initially occurs near the surface of the food load with internal heating (thawing) being a function of the degree of heat conduction through the food from the surface. Moreover, energy load-in at localized portions of the food, e.g. in the vicinity of a bone, can actually cause the food to become fully cooked at these locations while other portions of the food load are still frozen. Finally, as with room temperature thawing, it is necessary to insure that the thawed food is promptly cared for to avoid spoilage.
Commercial electromagnetic energy food thawing units are available that operate satisfactorily at lower frequencies, however, they are not practical for household use. They generally are found in high volume operations with employees in attendance to take the food and place it into a food preparation process immediately upon thawing.
There is, therefore, a need for a reliable, low cost food thawing apparatus suitable for household use. There is a need for such an apparatus that does not require constant attendance to avoid food spoilage and for an apparatus that uniformly thaws the food load without excessive heating or even cooking of localized portions of the food load before complete thawing is achieved.